Theory of Bose condensation of photons in nonequilibrium systems

In analogy with the theory of an ideal Bose gas, the spectrum and distribution function of photons in a semiconductor laser are studied on a model taking into account photon decay in the resonator and the action of a pump source. It is shown that coherent interaction of the photons of the central mode (condensate) with the active medium leads to the generation of supercondensate photons, which under certain conditions form new coherent modes. Line broadening of the laser radiation is another consequence of this interaction.